Herein, cross-compatibility means upward and downward compatibility. Upward compatibility is realized when new receivers accept and understand data transmitted according to an old protocol by old transmitters; and downward compatibility is realized when old receivers accept and understand data transmitted according to a new protocol by new transmitters.
Home control systems conventionally comprise actuators with associated sensors forming receivers of commands controlled by control units or control points forming command transmitters. In the following, “transmitter” refers to a device which is able to transmit control data and “receiver” to a device which is able to receive and interpret control data. The receivers are linked to actuators, for example electromechanical actuators, in order to transform the command received into an action on an element of the home control system. The transmission of data between the transmitter and the receiver conventionally occurs via a radio frequency link, although other transmission media are possible, such as for example an infrared link.
The transmitters and receivers can be mobile or fixed and comprise an autonomous power supply, for example from batteries. A fixed receiver can itself be powered by batteries or by means of photovoltaic cells for example, if it is linked to an autonomous actuator, which avoids wiring; and the reception function can be activated by a control or intermittently in order to limit power consumption.
The data transmitted between a transmitter and a receiver contain information relating to the nature of the control, the identification of the receiver and of the transmitter and other information such as data relating to the encryption, the history of the controls transmitted and the verification of the integrity of the transmitted data. The transmitted data are organized in a predetermined manner by a protocol. By protocol is understood a set of specifications describing conventions and rules to be followed in a data exchange. The protocols serve to guarantee efficiency in the data exchanges.
Certain existing protocols use fixed-length frames and all of the bits of the frame are exploited. This is the case for the RTS protocol (Radio Technology Somfy®) used in the home control systems installed by the applicant.
In such a situation, in order to allow a development of the functionalities for new products, it is common to construct a new protocol in which all of the existing or recently studied functionalities are taken into account and which provides bytes available for future developments. The drawback of a new protocol is generally its non-compatibility with the already installed products, not to mention the development costs generated.
Document WO 92/01979 discloses an extension of a wireless communication protocol to change from fixed codes to rolling codes, which equates to an increase in the number of possible addresses for the protocol.
The old frames comprise messages of ten word of 4 bits each. Two consecutive frames are separated by pauses (blank spaces) of 39 bits. Each start of the frame is signalled by a synchronization bit. In the case of a radiocommunication between a transmitter and a receiver, the frame is repeated a certain number of times, as long as the pressure on the transmitter button which is the origin of this transmission is maintained. The frame transmission durations are in fact generally much shorter than the duration of a manual pressing of the button. The receiver recognizes the transmitted format by detecting a synchronization bit following a blank space and it records the 10 word message sent.
The new frames comprise signals of twenty words, divided into two messages of ten words. Each message of ten words is transmitted in the traditional manner, i.e. as an old frame with blank spaces separating the two messages. The synchronization bit of the second message is however modified in comparison with the first. Each part of the message is recorded successively by the receiver. The synchronization bit of the second message serves to identify whether it is a second part of the message, and therefore a new generation frame, or another old generation message (repetition of the frame or frame with a different content).
Document WO 01/31873 discloses an extension of a protocol for frames of fixed length and with a predetermined content. This patent application describes the state of the art mentioning that the known protocol extensions allowing a downward compatibility consist of providing an explicit mechanism indicating an extension of the frames, for example by an indication of the frame length, an encoding of the indicator or reserved data. These known methods cannot be applied systematically and in particular cannot be applied in the case of a protocol with fixed-length frames, in which all the bits are used or reserved. According to the solution presented in this document, the field extensions are not attached to existing fields of the protocol, but placed elsewhere in the message.
Document WO 98/34208 describes a system for managing the compatibility between an old generation of products using an infrared transmission and a new generation of products using a radio frequency transmission. Downward compatibility is defined as the case where the old generation products only consider part of the transmitted data for their functioning but all of the data for the calculation of a sum for the purposes of verification, known as a “checksum”. The new generation protocol must maintain the checksum as the last data transmitted in order to retain this compatibility. The upward compatibility is provided by the control of the number of items of data transmitted and the determination of the corresponding type of protocol by the new generation receivers. In this system, the data inside the frame are reorganized and do not follow after an old frame.
The protocol extensions described in the above-mentioned documents WO 01/31873 and WO 98/34208 require adaptations of the frames of the existing protocol.
Moreover, the protocol extension described in the above-mentioned document WO 92/01979 can interfere with the reception of a message by old generation receivers. The complementary information is not integrated into the same frame and the flow of transmission (cyclic repetition of the frames and the inter-frame intervals) of messages which can be read by the old generation receivers is not the same depending on whether it is a transmission from an old or new generation transmitter.